1. Field of the Invention
The invention relates to polymer supported transition metal catalysts useful for the polymerization of olefins. More specifically, the catalysts are supported heterometallocenes and comprise a transition metal coordination complex having at least one anionic, polymerization-stable heteroatomic ligand and a boron compound activator on a particulate polymer support. The polymeric supports are ethylene homopolymers and copolymers of ethylene and C.sub.3-8 .alpha.-olefins.
2. Description of the Prior Art
The ability of metallocene catalysts to produce polyolefin resins of narrow molecular weight distribution (MWD), low extractables and uniform comonomer incorporation has spurred activity with these and other single-site catalyst systems. As used herein, single-site catalysts refer to transition-metal catalysts having one or more polymerization-stable cyclopentadienyl (Cp) ligands, Cp derivative ligands, heteroaromatic ligands or constrain-inducing ligands associated with the transition metal and which, when used to polymerize .alpha.-olefins, produce resins having the characteristic narrow MWD (M.sub.w /M.sub.n).
While single-site catalysts have been incorporated on supports for use in gas phase, slurry and related processes, reactor fouling and/or sheeting and reduced activity are problems. Fouling results in poor heat transfer, poor polymer morphology and, in extreme circumstances, can force reactor shutdown. Numerous procedures have been proposed to reduce reactor fouling and sheeting. For example, electrical methods have been proposed to control static electricity and antistatic agents have been included in the polymerization for this purpose. Surface treatments of the interior walls of polymerization vessels have also been employed. Various other techniques, such as the use of surface modifiers for the support material used, have also been utilized during catalyst preparation.
New supported single-site catalyst systems capable of reducing polymer stickiness and eliminating or minimizing reactor fouling are constantly being sought particularly, if the catalysts are derived from readily available and economical materials and if catalyst is not adversely affected. These and other objectives are achieved with the supported catalysts of the invention wherein a heterometallocene catalyst and boron compound are supported on a particulate polyethylene resin.
The use of polymer supports with Ziegler-Natta catalysts is known. For example, in U.S. Pat. No. 3,925,338 Ziegler-Natta catalysts are deposited on different particle size polyethylene supports to control the particle size in gas phase polymerizations. The use of vanadium catalysts supported on various speroidal high molecular weight polymers is disclosed in U.S. Pat. No. 4,098,979. Hoff, in U.S. Pat. Nos. 4,268,418 and 4,404,343 discloses the use of polymeric carriers, preferably containing a small amount of polar groups, as catalyst support. Carboxyl group-containing polymers modified with magnesium are used to support polymerization catalysts in U.S. Pat. No. 5,409,875.
Polymeric supports have been used as a means of attaching metallocene catalysts to the support. In U.S. Pat. No. 5,492,985, a polymer bound cyclopentadienyl ligand is reacted with a metallated polystyrene to obtain a polymer bound metallocene catalyst useful for olefin polymerizations. In a similar approach, metallocene catalysts tethered to a copolymer support, are disclosed in U.S. Pat. No. 5,587,439. U.S. Pat. No. 4,921,825 discloses a process for forming a solid catalyst by reacting a metallocene, such as bis(cyclopentadienyl)zirconium dichloride, with an aluminoxane in the presence of a particulate organic or inorganic carrier. Similarly, the reaction product of a metallocene with an aluminoxane or a microporous polymeric support is disclosed in EP 563917-A1. In all of the foregoing, the metallocene is either reacted with the support via functionality present on the support material or the metallocene compound is reacted with an aluminoxane. Moreover, none of the references disclose the use of heterometallocenes.